This invention relates to a system and method for detection of aural signals, and more particularly to an alert system for use by audio impaired automobile drivers which is responsive to an alarm siren sounded by an emergency vehicle to warn the hearing impaired driver so he can take appropriate action. The invention further relates to traffic light pre-emption by which an emergency vehicle, by rounding its siren as it approaches an intersection, causes the light to stop other vehicular traffic while providing a right-of-way to the emergency vehicle.
Many individuals who are hearing impaired are fully competent to drive an automobile, truck, or other vehicle. And, many of these people do drive. In normal circumstances, the visual aids such as street signs, traffic lights, road markings, etc., enable these people to drive safely. One situation however, is particularly dangerous to these persons. That is the presence of emergency vehicles carrying out their tasks. Police cars, fire trucks, ambulances all have both warning lights and sirens. Also for non-hearing impaired drivers, driving a car with the windows rolled up with the air conditioner blower on high, and with the radio on, it is also difficult for such persons to hear emergency vehicle warning sirens. While such drivers may see the flashing lights these emergency vehicle use in a time of emergency, in many emergency situations, such drivers are not able to see an emergency vehicle approaching and take appropriate action to avoid injury to himself and others. Enough situations arise where the emergency vehicle's flashers cannot be seen by the hearing impaired driver (the vehicle is approaching from a side street, or from an approach ramp above or below the driver's field of vision) that tragic consequences result.
While the problem is understood, a solution is not obvious. In any alarm system, there are at least two goals which must be met. One is that the probability of detecting the dangerous condition is high. The second is that the probability of false alarms is low. For example, it would appear simple, at first glance, to have some type of audio sensor which is responsive to a siren and provide a light indication readily recognizable by the driver when the sensor picks up an approaching siren. However, there are many different types of sirens and they do not have common characteristics. A major difference between them is the time-frequency pattern of their audio output; e.g., their rising/lowering pitch over time. One siren, for example, has a smoothly rising and falling pitch with a 4-5 second cycle time. A second siren has the same frequency variations as the first, but a much shorter cycle time (1/3 sec.). A third siren cycles between two frequencies every one-half second, with a fourth siren doing this at an even faster rate. As a result, a simple pattern matching technique cannot be used.
A second problem is with the sensor itself, which is some type of microphone or other audio receiver. Some microphones work well for one siren but not others. Others work better in open areas, other in more confined urban areas such as downtown areas with tall buildings. In this latter regard, tall structures produce echoes, and their resulting acoustic effect, together with that caused by wind, trees, hills, automobile vibrations, etc. may cause the critical frequencies to be washed out. Other effects include in-band noise and harmonic distortions. With respect to wind, wind generated noise can obliterate all but the loudest siren noises; i.e., those sounds which are 95dB or less. Overall, there is a need for an alert system for the hearing impaired which is able to detect any siren in use, do so in any area where the driver may go, and do so quickly enough that the driver can take the correct evasive action.